Why does the aluminum design wall panel sheet deform?
1. The plate has no edge rib and middle rib, which causes deformation under wind pressure and air tension.
This deformation phenomenon often occurs on the curtain wall with aluminum-plastic composite plate as the panel. In order to save money, building owners choose informal manufacturers. In order to obtain higher profits, manufacturers do not use any side ribs and middle ribs. Fold the aluminum-plastic plate into a box shape, screw it directly on the frame with screws, and apply glue to the plate gap. In this way, the plate strength of the curtain wall is not enough at all, and the plate produces inward and outward fatigue deflection deformation under the action of positive and negative wind pressure, which increases the size of the plate surface. For the curtain wall reflecting the more prominent sunny side, because the construction process adopts the form of thermal insulation and warm wall to seal all the plate gaps with glue, the air in the interval between the plate surface and the structural wall heats up under the sunshine effect, and the plate deforms outward under the action of air expansion.
2. The plate and curtain wall structure frame are fixed, and the thermal stress cannot be released, resulting in deformation.
The aluminum plate curtain wall is located in areas with a large seasonal temperature difference. In the season with low temperatures at the end of spring and autumn, the thermal effect of sunlight is very strong, especially for aluminum plates with darker color. The temperature rises greatly, and the thermal expansion value of aluminum plates per meter length is large at different temperatures.
The curtain wall frame is inside, and the influence of sunlight is weak. When the aluminum plate and the frame are at the maximum, the temperature difference of more than 80 ℃ can be generated. When the aluminum plate size is large, there will be a large linear expansion difference. If the curtain wall plate structure adopts the structure of folding and fixing the aluminum plate on the frame with screws, the thermal stress on the aluminum plate surface will not be released, forcing the plate surface to yield and deform outward under the action of air.
This deformation phenomenon is quite large, especially when the curtain wall frame in the aluminum plate adopts a steel profile, because the thermal expansion coefficient of aluminum is generally twice that of steel, the deflection of plates with the same size will be twice that of the values in the table.
It is found that some manufacturers process the screw holes of the fixed plate into long holes along the length or width direction of the plate on the corner code of the fixed plate, but the plate is still deformed after installation, and this connection method can not meet the requirements of deformation in the plane of the curtain wall.
3. Stress deformation occurs during the assembly of panel and side rib
In order to solve the thermal stress and deformation of the aluminum plate surface, some manufacturers, particularly when the aluminum-plastic composite plate is used for the panel, add a ring of edge rib frame around the unit plate. From the production process, the panel is grooved and folded into a box shape on the grooving machine according to the plate folding size. The other line is to cut the edge rib profile according to the required size of the plate and assemble it into an edge rib frame. Then install the side rib frame into the box panel and fix the two bodies with pop rivets. It is commonly found at the work site that due to the deviation of the panel groove folding, the deviation of the edge rib profile assembled into the frame, and the matching of the two bodies often occurs that either the frame is tiny or the plate folding size is too big. In order to ensure the construction period and no material consumption, assembly is frequently forced, resulting in assembly stress on the plate surface, either edge rib deformation or plate surface compression deformation. This kind of plate deforms outward under the action of temperature and air expansion force.
Rectification measures for deformation of aluminum plate curtain wall
The most basic principle of curtain wall product design shall be that, in addition to ensuring the strength, the structural design of embedded body shall be adopted for both structural frame and finish, and thermal stress shall not be allowed. If thermal stress is generated, the member will be deformed and damaged. In order to avoid thermal stress, a certain gap must be left at each matching part. The designer must have appropriate structure or sealing materials to ensure the air tightness and water tightness of the product. This is the key to the success of curtain wall design.
1. Aluminum curtain wall plate and frame must be floating connection
Since China's reform and opening up, all aspects have undergone rapid changes, particularly the construction industry. New buildings have sprung up everywhere, and they are getting higher and higher. In order to meet the curtain wall used in super high-rise buildings, from the structure: first, it can not generate thermal stress; second, it should meet the requirements of in-plane deformation of curtain wall caused by natural vibration and increased amplitude under wind load of super high-rise buildings. Moreover, in the seismic design, it should be designed according to 3 times of the displacement control value calculated by elasticity of different building structure types. For example, in the earthquake fortification area, there is a super high-rise building with frame structure with interlayer height of 3.4m, and the displacement of curtain wall must meet the requirement of 25.5mm. This requires that the curtain wall plate must be floating connected with the structural frame on the premise of meeting the strength requirements. These two sketches are only a form of plate connection, and a variety of structures can be designed in product design. However, no matter what form of structure is adopted, the design principle is that the plate connection structure must be able to absorb the thermal stress caused by temperature difference and the in-plane deformation requirements caused by earthquake.
2. Aluminum curtain wall plate eliminates assembly stress
If the plate of aluminum curtain wall is not ribbed, the corner code welded, riveted or directly stamped on the plate is used. That is, the fixing screw hole of the corner code is opened with long holes, which can not solve the deformation problem caused by thermal stress. There are numerous plates used in a project, and some of the plate sizes vary considerably. The maximum thermal expansion of the plate varies with the length and width of the plate. It does not change along the length width direction of the board, but according to the tangent function value of the triangular function. It is impossible to calculate the possible expansion direction of each corner code on the periphery of each board for engineering by using the computer according to the location of the board where the corner code is located, and open the inclined long hole of each corner code according to this direction. Another factor is that the screws for fixing the plate must be tightened. When the aluminum plate has no edge ribs, the strength at the hem is feeble, so it is hard to transfer the thermal stress to the corner code, so that the corner code can creep according to the temperature difference to absorb the thermal expansion. Therefore, this method of opening long holes on the corner code can not solve the problem of aluminum plate deformation.
In order to solve the problem of no deformation of aluminum plate, the plate and frame structure must be floating connection. In order to transfer the thermal stress to the folded edge of the plate, edge ribs must be added at the folded edge of the plate for reinforcement, that is, 3mm thick single aluminum plate shall be used for reinforcement in areas with large seasonal temperature difference. In order to ensure that the folded aluminum plate does not generate assembly stress in Figure 3 and ensure the manufacturing quality of aluminum plate, the side rib frame shall be designed as a tall and wide retractable structure. In terms of tolerance and fit terms, the size of the plate folded into a box is the reference hole, which is matched with the folded plate by the expansion of the side rib frame, and the four corners of the side rib frame are connected by connectors. 2mm clearance shall be reserved at both ends of the horizontal and vertical bars and connectors of the side rib frame, and the length and width of the frame shall be adjusted to 4mm, which is sufficient to absorb the processing deviation of the plate folding and frame assembly, and eliminate the phenomenon that the inappropriate cooperation in Figure 5 affects the quality. The retractable side rib frame not only strengthens the thermal stress conduction, but also absorbs the thermal stress deformation caused by the small temperature difference in the panel, so as to eliminate the deformation of the aluminum plate and ensure the flatness of the entire aluminum plate curtain wall.
3. The reinforcing middle rib of the aluminum curtain wall plate shall be floating connection
There are about three ways to connect the reinforcing middle rib of aluminum curtain wall plate with the panel: structural adhesive bonding, super adhesive tape bonding and planting welding screw fixation. Their common feature is to fix the middle rib and the panel, and most of the two ends of the middle rib are fixed with the side rib frame.
The panel is directly exposed to the sun, and the reinforcing rib is inside the panel. Especially after a layer of adhesive is isolated, thermal stress occurs with the panel due to temperature difference, which limits the expansion of the panel along the axial direction of the reinforcing rib. If both ends of the reinforcing rib are fixed with the frame rib, the expansion of the panel along the radial direction of the reinforcing rib is limited, which is easy to cause shear damage of the adhesive and connector and reduce the durability life.
Reinforcing the middle rib and plate of aluminum curtain wall plate; fix the two ends of the high-strength rib with one of the reinforcing screws in the middle frame, and then fix the reinforcing rib with one of the three reinforcing screws along the length of the middle frame. Note that 2mm gap shall be reserved between the upper part of the reinforcing middle rib and the pressing plate, and 2mm gap must also be reserved between the end of the reinforcing middle rib and the corner code. This floating connection structure will not generate thermal stress between the panel and the middle rib, which not only achieves the reinforcing effect, but also ensures the flatness of the panel.